1. Field of the Invention
This invention relates to tool couplers which hold the shank of an elongated tool and, more particularly, to tool couplers, or chucks, which hold rotating tools such as drill bits.
2. Prior Art
The most popular prior art couplers, or chucks, are those which are used on most power drills. The shank of the tool or bit is held in place by a friction grip, which is adjusted using a key. If the grip is not adequately tightened with the key, the grip on the shank will slip, necessitating retightening of the chuck. More importantly, the user of such a coupler must keep track of the location of the key, or the device is useless. Misplaced keys are a constant problem. Also, the time required to change bits is lengthy, due to the time required in loosening and tightening the grip on the shank.
Some devices have been designed to drive a bit having a shank of non-circular cross-section. Such shanks, usually having square or hexagonal cross-sections, may be driven by chucks which have matching sockets, eliminating the need for a friction grip and thus the key. It is necessary, however, in such devices to maintain some grip on the shank in order to hold the shank longitudinally within the chuck. This is usually accomplished by use of a spring-loaded sleeve, which urges one or more balls against the drill shank, holding it in place. Such devices are operated by positioning the sleeve with one hand to loosen the grip of the balls, and either inserting or removing the bit shank with the free hand. The drill or other rotative power tool must be released and manipulated in order for the user to operate the chuck with both hands. This process is time-consuming and cumbersome.